The present invention relates to a bearing which is capable of receiving a radial load, axial loads in two directions, and a moment load and also which is usable in an industrial machine, a robot, a medical instrument, a semiconductor/liquid crystal manufacturing apparatus, an optical instrument, an opto-electronic instrument, and so on.
Conventionally, as a bearing which is capable of receiving a radial load, axial loads in two directions, and a moment load, there are known a cross roller bearing and a four-point contact ball bearing. In the conventional cross roller bearing, between an inner race 100 and an outer race 200, there is incorporated a cylindrical-shaped roller 300 (see FIG. 18). On the other hand, in the conventional four-point contact ball bearing, between an inner race 100 and an outer race 200, there is incorporated a ball 400 (see FIG. 19).
However, in the conventional cross roller bearing and four-point contact ball bearing, there are found the following problems to be solved.
(1) In the case of the cross roller bearing, since a rolling element is a cylindrical-shaped roller 300 and the rolling contact surface 301 of the roller 300 is line contacted with a raceway groove 500, there is produced large torque.
(2) In the case of the four-point contact ball bearing, because a rolling element is a ball, when the bearing receives a pure axial load or when an axial load is dominant over a radial load, the four-point contact ball bearing produces smaller torque than the cross roller bearing of the same size. On the other hand, when a radial load is dominant over an axial load or when the bearing receives a pure radial load, each ball 400 is contacted with a raceway groove 500 at four points 401, 401, 401 and 401 and, therefore, there occurs large spin slippage between the ball 400 and raceway groove 500, which results in large torque.
The present invention aims at solving the above problems found in the conventional cross roller bearing and four-point contact ball bearing. Accordingly, it is an object of the invention to provide a rolling bearing which can control spin slippage between a rolling element and a raceway groove and can reduce rolling resistance to realize low torque, thereby being able to receive a radial load, axial loads in two directions, and a moment load.
In attaining the above object, according to the invention, there is provided a rolling bearing, wherein a plurality of rolling elements are incorporated between a pair of races, each of the two races has a raceway groove defined by two raceway surfaces each having a radius larger than the radius of each of the rolling elements, the outside diameter of each rolling element serving as the rolling contact surface thereof has a curvature in the axial direction of the rolling element as well, the mutually adjoining ones of the rolling elements are arranged in such a manner that they cross each other alternately, and the outside diameter of each rolling element is always contacted at two points with the raceway surfaces of one of the races as well as with the raceway surfaces of the other.
The above-mentioned object can also be achieved by a rolling bearing, according to the present invention, comprising:
a first race having a race way groove defined by two raceway surfaces;
a second race mated with the first race, the second having a race way groove defined by two raceway surfaces; and
a plurality of rolling elements rotatably incorporated between the first and second races, each of the rolling elements having a rolling contact peripheral surface defined by rotating a curved bus line about its rotation axes, the curved bus line having a sole predetermined curvature which is smaller than any one of the radius of raceway surfaces of the first and second races,
wherein the rolling contact surface of each of the rolling element is always contact contacted at two points with the raceway surfaces of the first and second races, the two points are consisted of a first point positioned at one of the two raceway surfaces of the first race and a second point positioned at one of the two raceway surfaces of the second race, and the mutually adjoining ones of the rolling elements are arranged in such a manner that their rotation axes each other alternately.